1. Field of the Invention
The present invention relates to a method of determining an amount of exposure, and in particular, to a method of determining an amount of exposure in which when a color original image is copied onto a color copy material or a black-and-white copy material, density data of a human face is extracted, and an amount of exposure is determined on the basis of the extracted density data.
2. Description of the Related Art
When a photograph of a person is viewed, the area which is most noticed is the person's face. In order to produce high-quality photographs or images, it is necessary to print or display the color of a human face at an appropriate color.
Conventionally, when an image containing a person is printed or displayed at a printer, a printing device, or a photographic processing apparatus such as an image display device, face density data is extracted. On the basis of the extracted density data, the face density is reproduced as an appropriate density which is a target density, and an amount of exposure is determined so that the color of the face can be printed or displayed appropriately.
However, this method presupposes that there is a single reflectance of human faces. In a color image, when there are faces of a plurality of different reflectances which differ due to individual differences or differences between races, a drawback arises in that there is a dispersion of face densities, and correction for printing or displaying at appropriate colors in accordance with the face densities cannot be effected.
In order to solve this drawback, a system has been proposed in which correction is effected by using the average value of the densities of a plurality of faces as the face density. However, as is well-known, the reflectances of faces differ greatly among different races. Namely, as illustrated in FIG. 14, in the spectral reflectance characteristic of skins of six races from Caucasian to Negro, (in FIG. 14, Z1: blond Caucasian, Z2: brunette Caucasian, Z3: Asian, Z4: Hindu, Z5: mulatto, Z6: Negro) there is a difference of seven to eight times between Caucasians and Negroes (from the Japan Color Society, "Color Science Handbook: New Edition", Chapter 28: Skin Colors and Make-up Colors, Tokyo University Publishing Group, page 1097, 1985). Accordingly, when correction is effected by simply using the average value of the densities of a plurality of faces as the face density, there is a drawback in that the densities of some of the faces will not be finished at the appropriate density.